G01P3/42—Devices characterised by the use of electric or magnetic means

G01P3/44—Devices characterised by the use of electric or magnetic means for measuring angular speed

G01P3/46—Devices characterised by the use of electric or magnetic means for measuring angular speed by measuring amplitude of generated current or voltage

G01P3/465—Devices characterised by the use of electric or magnetic means for measuring angular speed by measuring amplitude of generated current or voltage by using dynamo-electro tachometers or electric generator